The next time you go to calibrate your CO2 sniffer you now have an even round number to work with. Ambient CO2 has just crossed the threshold to 400 parts per million, according to NOAA. For those keeping track, this is the first time since the Miocene period, 800,000 years ago that we’ve reached this level of CO2! Read more here. If you are curious how your favorite plants respond to increased CO2 concentrations, you can look up the increase in performance by either photosynthesis or dry mass of specific plants here. Unfortunately, cannabis is not one of the plants listed.